The present invention relates generally to continuously variable transmissions for motor vehicles, and more particularly, to a four-wheel drive continuously variable transmission.
In general, power transfer mechanisms, such as transfer cases, are operative for selectively directing power to the non-driven wheels of a motor vehicle for establishing four-wheel drive modes. Many automotive transfer cases are equipped with a speed reduction gear assembly for providing xe2x80x9chighxe2x80x9d and xe2x80x9clowxe2x80x9d speed ranges in conjunction with two and four-wheel drive modes. As such, a range shift mechanism is provided for operatively shifting components of the speed reduction gear assembly between a high range position providing a direct ratio drive connection and a low range position providing a reduction ratio drive connection.
Conventionally, transfer cases are provided in combination with standard automatic and manual transmissions. However, conventional automatic and manual transmissions are heavy and contribute greatly to the weight of the vehicle and are only capable of establishing discrete gear ratios. Furthermore, automatic transmissions are inefficient due to the requirement that the hydraulic system utilized for controlling the sequential shifting of the automatic transmission requires a large amount of power in order to maintain the hydraulic fluid pressure even when shifting is not necessary. Thus, it would be desirable in the art of automotive transmissions to provide a four-wheel drive transmission which has improved efficiency, a continuously variable operating range, and reduced size and weight.
Accordingly, it is an object of the present invention to provide a four-wheel drive transmission which combines a continuously variable transmission unit and a transfer case unit into a common assembly.
It is another object of the present invention to provide a four-wheel drive transmission which is lighter in weight and more compact than conventional transmission and transfer case combinations.
It is still another object of the present invention to provide a four-wheel drive transmission which does not require an engine clutch.
A further object is to provide a rear-wheel drive transmission integrating a continuously variable transmission unit and a geared drive selector unit into a common assembly. A related to object is to arrange the continuously variable transmission unit and the geared drive selector unit to provide a front-wheel drive transaxle.
These and other objects of the present invention are obtained by providing a four-wheel drive transmission having a continuously variable transmission unit, a planetary drive selector unit, and a torque transfer unit. The four-wheel drive transmission is further equipped with a worm/worm gear transmission which is controlled by a transmission controller to provide continuous ratio control of the continuously variable transmission unit.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood however that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.